help please, i have just had a ariston micro genius 28he combi fitted , thier is a rattel / buzzing noise coming from the diverter valve / chr pipe area when the pump is on mark 3 , when you turn the pump to 2 the noise gose quieter and when on mark 1 you canot here anything, this noise dose not happen when hot water is called for only on ch, the hw and ch are both working fine, my gas engineer says its because i have 22mm goining into 15mm then into 10 mm pipes running on my central heating and thiers to much pressure with the pump on mark 3, could someone confirm this to be true as iam not convinced ,thank you gareth